Hydroalkylation of mononuclear aromatic hydrocarbons

ABSTRACT

HYDROALKYLATION OF MONONUCLEAR HYDROCARBONS IS EFFECTED UNDER CONTROLLED CONDITIONS TO YIELD PRODUCT HYDROALKYLATE WITH MINIMUM OF FORMATION OF UNDESIRED BYPRODUCTS.

United States Patent Filed Dec. 6, 1972, Ser. No. 312,441 Int. Cl. C07c5/12 U.S. Cl. 260--668 R 14 Claims ABSTRACT F THE DISCLOSUREHydroalkylation of mononuclear hydrocarbons is effected under controlledconditions to yield product hydroalkylate with minimum formation ofundesired byproducts.

BACKGROUND OF THE INVENTION This invention relates to hydroalkylation.More speciiically it relates to the selective hydroalkylation of benzeneto permit attainment of high yields of cyclohexylbenzene.

As is Well known to those skilled in the art, it is possible tohydroalkylate aromatic, preferably mononuclear, hydrocarbons such asbenzene, by the reaction with hydrogen in the presence ofhydroalkylation catalyst under hydroalkylation conditions to yieldproduct hydroalkylate. This product primarily contains cyclohexylbenzeneand the ortho-, meta, and para-isomers of dicyclohexylbenzene.

It is an object of this invention to provide a process forhydroalkylation. It is another object of this invention to provide aprocess for hydroalkylating a charge benzene to producecyclohexylbenzene. Other objects will be apparent to those skilled inthe art.

SUMMARY OF THE INVENTION In accordance with certain of its aspects, thenovel process of this invention for hydroalkylating a charge mononucleararomatic hydrocarbon with a hydroalkylating quantity of hydrogen maycomprise:

passing said charge hydrocarbon and a first portion of saidhydroalkylating quantity of hydrogen through a lfirst hydroalkylationoperation at hydroalkylation conditions thereby forming a partiallyhydroalkylated stream;

withdrawing said partially hydroalkylated stream from said firsthydroalkylation operation;

passing said partially hydroalkylated stream through at least onesubsequent hydroalkylation operation at hydroalkylation conditions;

passing the remainder of said hydroalkylating quantity of hydrogen tosaid subsequent hydroalkylation operation;

maintaining said partially hydroalkylated stream, during passage intoeach hydroalkylation operation, at hydroalkylation conditions therebyforming a product hydroalkylate; and

withdrawing product hydroalkylate from the last of said hydroalkylationoperations.

DETAILED DESCRIPTION OF THE INVENTION The charge mononuclear aromatichydrocarbons which may be hydroalkylated by the process of thisinvention may include benzenes, including substituted benzenes, such asbenzene se, toluene, xylenes, etc. The preferred charge may be benzenese.

Hydroalkylation may preferably be effected in one embodiment by passingto the hydroalkylation operation a charge mononuclear aromatichydrocarbon, typically benzene, together with recycled materials,typically dicyclohexylbenzenes. Among the latter may be ortho-di- ICCComponents Parts Typical B Amena 40-99. 5 92. 5 Cyelohexylbenzene i 0-50. 6 Ortho-dieylohexylbenzene] meta-dloyclohexylbenzene] 0. 5-15 5. 2Para-dicyelohexylbenzene 0-15 1. 6 Methyl cyelopentane 0-10 0Cyclohexane 0-15 0 Other components may be present, including methylcyclopentyl benzenes, bicyclohexyl, tricyclohexyl benzenes, etc.

Preferably 100 parts by weight of benzene and a hydroalkylatingquantity, preferably 0.21-10 parts, more preferably 0.2-3 parts, say 1.1parts by weight of hydrogen may be employed for hydroalkylation.

Hydroalkylation may be effected in the presence of a hydroalkylationcatalyst and a hydroalkylating quantity of hydrogen. The hydrogen neednot be pure; but preferably hydrogen of %-100% purity may be used. Thehydrogen should preferably be free of any impurities which may poisonthe catalyst. Hydrogen recovered from a reforming operation may besuitable.

The catalyst may contain a Group VIII transition metal component, e.g.,cobalt, nickel, ruthenium, rhodium, palladium, iridium, and platinum.The preferred type of catalyst may include a Group VIII metal, typicallynickel or cobalt; and it may also contain 0-30%, typically 10%- 20%, say19% of a Group VI metal, typically tungsten, on a silica-aluminacatalyst support. When the Group VIII metal is Co or Ni, it willpreferably be present in an amount of 2%-30%, typically 4.0%-25%, say22%. When the Group VIII metal is a noble metal, it may be present inamount of 0.2%-5%, say 1%. Such a catalyst may be prepared for exampleby impregnating or ionexchanging a commercial NH4-exchanged Y zeolitecatalyst with e.g. nickel nitrate (or cobalt nitrate) and thereafterwith ammonium metatungstate solution and then drying the catalyst in airat say C. The so-dried catalyst may be further dried at C. and thencalcined to a maximum temperature up to 800 C.

The catalyst may be calcined during which residual nitrates aredecomposed and the catalyst is dehydrated. The catalyst may (preferablyafter loading into the hydroalkylation unit) be reduced in the presenceof hydrogen for a minimum of l hour and typically at least 4-8 hours ata temperature preferably above about 300 C. and typically 300-700 C.,say 500 C.

The so-prepared typical catalyst may contain, on a dry basis, 6% nickel,19% tungsten, and 22% hydrogen-Y zeolite, the remainder being amorphoussilica-alumina support.

Hydroalkylation of aromatic feed may be effected by using this catalystat an LHSV of 1.0-15, typically 2-10, say 3.

The pressure of hydroalkylation may typically be 100- 1500 p.s.i.g.,preferably 100-500 p.s.i.g., say 500 p.s.i.g.; at this pressure thereactants are maintained substantially in liquid phase-except' for thehydrogen which is in gas phase.

It is a feature of the novel process of this invention thathydroalkylation be carried out in a plurality of (including a first andat least one subsequent) hydroalkylation operations or stages. Eachoperation may be carried out in a separate portion of a single reactionvessel or, as is more preferred, in a separate reaction vessel.Typically there may be 2-10 separate hydroalkylation operations,commonly 2, each carried out in a separate reaction zone or vessel. Thepartially hydroalkylated effluent from the first hydroalkylationoperation may be passed to subsequent hydroalkylation operations whereinadditional hydrogen is admitted and further hydroalkylation may occur.

The amount of hydrogen admitted to the first reactor may typically begreater than the amount calculated from the total amount of hydrogenadded in all the hydroalkylation operations divided by the number ofhydroalkylation operations.

In a preferred embodiment, hydroalkylation may be carried out by passingthe charge hydrocarbon and a rst portion of the hydroalkylating quantityof hydrogen through a first hydroalkylation operation at hydroalkylationconditions. In one preferred embodiment, hydroalkylation may be effectedin two operations; and the amounts of hydrogen admitted to each of thehydroalkylation operations may be substantially equal.

Typically, however, when two stages are employed, the hydrogen admittedto the tirst hydroalkylation operation may be greater than about 50%,e.g. 50%-70%, say 55%, of the hydroalkylating quantity of hydrogen; andthat admitted to the second hydroalkylation operation may be less thanabout 50%, e.g. 30%-50%, say 45%.

If hydroalkylation be carried out in three steps, the quantity ofhydrogen admitted to the rst zone may be 35%45%, say 40% of the totalhydrogen admitted; the quantity admitted to the second zone may be30%-35%, say 35% of the total; and the quantity admitted to the thirdzone may be %-30%, say 25%.

Typically the inlet temperature to the first operation may be lower thanthe inlet temperature to subsequent operations; and consequently morehydrogen may be permitted to react in the first zone or operationwithout exceeding a preferred upper limit of temperature. Generally thefresh charge benzene is more reactive than is the mixed hydroalkylationproduct; and thus a lower inlet temperature may be used in the lirsthydroalkylation operation.

Itis a feature of the process of this invention that each of thehydroalkylation operations be carried out at maximum operatingtemperature of less than about 250 C. (482 F.) and preferably at lessthan 210 C. (410 F.). Typically, temperature may be 100 C.210 C., say190 C. (375 F.) and the hydrogen partial pressure may be 50-1500p.s.i.g., preferably 100-1500, more preferably 100-700 p.s.i.g., say 500p.s.i.g.

The temperature of reaction may in one embodiment be controlled bycooling the feed to each hydroalkylation operation to a temperature of20 C.-150 C., preferably 40 C.-100 C., say 80 C. below maximum operatingtemperature. Thus the feed to a hydroalkylation operation I nay be at 80C.200 C., preferably 100 C.-190 C., say 125 C. As hydroalkylation occursin one hydroalkylation operation, the temperature rises within theoperating temperature range.

In an alternative embodiment, each hydroalkylation operation may becarried out in a reactor which includes means for heat transfer. Coolingmay be effected for example by passing the feed gases through a heatexchanger reactor wherein the reactants are cooled by indirect heattransfer against a cool heat transfer medium e.g., a gas which is cooledexternally.

It has unexpectedly been found that practice of the process of thisinvention permits recovery of product containing decreased proportionsof undesirable by-products, particularly when operating at lowertemperatures. In a typical series of comparative runs, benzene may behydroalkylated with hydrogen over a nickel-tungsten on a hydrogen formof zeolite Y catalyst (which catalyst is first reduced at 480 C. withhydrogen). It is found that,

as the average temperature of operation in each bed decreases from 200C. (400 F.) to 120 C. (250 F.), the weight ratio in the product streamof undesired byproduct methyl cyclopentane to desired by-productcyclohexane decreases from 2.0 to about 0.2; i.e. the composition of theproduct stream drastically changes from one containing only 33% desiredvby-product to one containing 83% desired by-product.

Similarly it is also found that impurities, which have boiling pointswithin the cyclohexylbenzene range (and which would thus be expected toappear in the fractionated cut containing product cyclohexylbenzene) aresubstantially reduced. Specifically the ratio of such impurities toCyclohexylbenzene may typically be decreased from about 0.12 at 205 C.(400 F.) down to less than 0.01 at 120 C. (250 R).

It will be apparent to those skilled in the art that results comparableto those noted may be achieved by the use of other catalyst systems.

As will be apparent, the composition of the hydroalkylate product willbe a function of the charge to the hydroalkylating operation. In oneembodiment, wherein the charge benzene is benzene se plus recycleorthodi- Cyclohexylbenzene, meta-dicyclohexylbenzene, andparadicyclohexylbenzene, the product may typically contain thefollowing:

In the preferred embodiment, the hydroalkylate product in amount ofparts may be passed, in liquid phase, to a separation operation whereinany hydrogen present may be flashed off.

The flashed product liquid may be preferably heated and passed to abenzene recovery tower. Typically 58.9 parts of benezene may berecovered as overhead and condensed against water. A portion of thecondensate is returned as pumped reflux to the benzene recovery tower;and the remainder of the recovered benzene may be recycled to thehydroalkylation operation, preferably after purification to remove e.g.C6 naphthenes.

41.1 parts of bottoms may be heated and passed, in the preferredembodiment, to Cyclohexylbenzene recovery tower. Overheadcyclohexylbenzene may be condensed against water; and a portion thereofmay be returned as pumped reflux to the Cyclohexylbenzene recoverytower.

Bottoms from the Cyclohexylbenzene recovery tower, in amount of 8 parts,may be heated and passed in the preferred embodiment of thedicyclohexylbenzene recov- `ery tower. Bottoms from thedicyclohexylbenzene recovery tower may typically include tricyclohexyl(and higher boiling) benzenes.

The overhead from the dicylohexylbenzene distillation operation mayinclude dicyclohexylbenzene; and typically this stream may include lessthan 10% of other components. It may be found that thedicyclohexylbeuzene fraction recovered as overhead from thedicyclohexylbenzene distillation tower may contain 0.5-15 parts, say 2.6parts of para-isomer and 0.2-15 parts, say 5.4 parts of the mixedorthoand meta-isomers.

4.Typically 8.0 parts of the dicyclohexylbenzene fraction may be cooledto minus 20 C. to plus 25 C., say minus 10 C. There may be preferablyadded to the fraction, prior to cooling, 1.6-4 parts, say 2.4 parts of adiluent, typically a lower alkanol such as isopropyl alcohol ormethanol. During cooling, the para-isomer may crystallize and separatefrom the orthoand meta-isomer which remain in the liquid phase. Thecooled mixture, a slurry of the solid phase para-isomer in liquid phasecontaining the orthoand meta-isomer and preferably diluent, may bepassed to a separation operation, typically a filtration operation.

In the filtration operation, conduct-ed at minus 20 C.- plus 25 C., sayminus 10 C., 0.2-10 parts, say 1 part, of crystals ofpara-dicyclohexylbenzene (containing typically 0.1-1 parts, say 0.2parts of mixed orthoand meta) are separated as filters cake from thefiltrate which contains 0.5-15 parts, say 5.2 parts of orthoandmeta-dicyclohexylbenzenes (and 0.1-4 parts, say 1.6 parts of para) andoptionally say 0.6 parts of cyclohexyl-benzene.

The filter cake may be washed with lower alkanol, typically isopropanoland recovered therefrom as by further filtration. Yield ofpara-dicyclohexylbenzene (filter cake) may be 0.2- parts, say 1 part.

It is possible to carry out to the process of this invention byadmitting to the hydroalkylation operation in the preferred embodiment0.5- parts, say 5.2 parts of dicyclohexylbenzene, preferablynon-para-dicyclohexylbenzenes. Preferably the dicyclohexylbenzeneadmitted to the hydroalkylation operation will contain less than 4parts, typically 1.6 parts (more preferably it will contain as little aspossible) of the para-isomer.

The stream of dicyclohexylbenzene admitted with charge benzene to thehydroalkylation operation may be essentially meta-dicyclohexylbenzene(in amount of 0.5- 15 parts, say 5.2 parts) or, less preefrably,ortho-dicyclohexylbenzene (in amount of 0.5-15 parts, say 5.2 parts).

The stream of dicyclohexylbenzenes admitted to the hydroalkylationoperation may include 0.5-15 parts, say 5.2 parts of mixed orthoandmeta-isomers in amount substantially equal to the amount thereof formedduring the hydroalkylation of benzene. In one embodiment, thedicyclohexylbenzene separated from the product hydroalkylate may, inwhole or part, be recycled to the hydroalkylation reaction.

It will be apparent to those skilled in the art that the novel processof this invention permits hydroalkylation to be carried out at lowtemperatures invmanner to yield high conversion to desired products,typically cyclohexylbenzene, with low yield of undesired naphthenes andof impurities boiling in the cyclohexylbenzene boiling range.

The use of intermittent addition of hydrogen, the hydroalkylation in thepresence of large excesses of e.g. benzene, and the temperature controlduring hydroalkylation permit attainment of desired results.

DESCRIPTION OF PREFERRED EMBODIMENT@ Practice of the process of thisinvention may be apparent to those skilled in the art from inspection ofthe following examples wherein as elsewhere in this specification, allparts are parts by Weight unless otherwise specitied.

Examples I-III In practice of the process of this invention according toone embodiment, hydroalkylation is effected by use of a catalyst,containing 6% nickel and 19% tungsten on silica-alumina supportcontaining 22% of the hydrogen form of zeolite Y, which had been reducedby contact with hydrogen for 2 hours at 370 C. (700 F.) and 500 p.s.i.g.During hydroalkylation, benzene is admitted to the reactor together with51% of the hydroalkylating quantity of hydrogen. At operating pressureof 500 p.s.i.g. (partial pressure of hydrogen), the nominal (inlet)temperature within the reactor is 190 C. (375 F.) and the temperaturewithin the catalyst bed 188 C.205 F. (370 F.- 400 E).

The product is collected over 63 hours; and it is then passed throughthe reactor a second time at inlet temperature of 188 C. (370 F.) with49% of the hydroalkylating quantity of hydrogen. The product iscollected and analyzed; the following table sets forth the total partsof hydrogen added per pass per parts of benezne, and also thecomposition, in terms of weight percent, of product collected (basedupon benzene feed) after the first and after the second pass.

rst; second Component pass pass Hydrogen added, parts 0.75 0. 71Methylcyclopentane, percent 1.1 2. 0 Cyclohexane, percent; 1. 6 2.8Cyclohexylbenzene impurities,\ percent-. 0.7 1.3 Cyclohexylbenzene,percent 15. 8 28. 4 Dieyclohexylbenzene impurities,1 percent 0.8Dicyelohexylbenzene, percent 3. 2 8. 6

l Impurities boiling in the eyclohexylbenzene boiling range. 2Impurities boiling in the dicyclohexylbenzene boiling range.

Examples IV-VIII In a second series of comparative examples,hydroalkylation of benzene was carried out over a catalyst (the same asthat of Ex. IIII) which had been reduced in a stream of hydrogen for 4hours at 482 C. (900 CE1). The charge benzene was dried by passagethrough silica gel and then over calcined 4A Zeolite (Linde molecularsieve); and it was charged at 2 LHSV together with deoxygenatedhydrogen. All the hydrogen (0.88 parts of hydrogen per 100 parts ofbenzene) was consumed. Initial pressure was 400 p.s.i.g., but as thecatalyst aged, the pressure rose to 500 p.s.i.g. Inlet temperature is C.(300 F.) with a rise of 160 C. (30 F.) in the catalyst bed. The productis collected over 4-96 hours.

This product is then passed through the reactor a second time at 2 LHSVand inlet temperature of 150 C. (300 F.) together with hydrogen asbefore but with hydrogen in amount of 0.40-0.69 parts per 100 parts ofbenzene originally charged. Product from the second pass is collected inthree aliquots: (a) 0-108 hours (Ex. V); (b) 108-116 hours (Ex. VI); and(c) 116-144 hours (Ex. VII). The following table sets forth thecomposition of the products collected, in terms of Weight percent ofproduct collected (based upon benzene feed) after the first pass and (a)after 108 hours, (b) 108-116 hours, yand (c) 11'6-144 hours. Alsoshowing is the total parts of hydrogen added per pass per 100 parts ofbenzene.

. Second pass First pass 0-108 108-116 116-144 Component 1v h., v n., vrh., vn vnr Hydrogen added... 0. 88 0. 39 0. 68 0. 66 1. 39 Benzene", 72.7 62. 5 53. 4 53. 9 56. 2 Methyl cyclopentane O. 15 0. 27 0. 23 0. 24 1.2O Cyelohexane 2. 87 4. 44 5. 37 5. 23 3. 60 Cyelohexylbenzeneimpurities 0. 2 0. 4 0. 5 0. 5 1. 1

Cyclohexylbenzene 20. 8 25. 9 31. 3 31.0 32. 5 Dicyclohexylbenzene- 3. 36. 8 8. 9 9. 0 6. 4

It will be apparent from comparison of Example VII (at 150 C.) withExample II (at 188 C.) that in practice of this invention, operation atdecreased temperature permits recovery of the desired cyclohexylbenzenewith decreased amounts of cyclohexylbenzene impurities (e.g. 0.5/31.0 or1.6% v. 1.3/28.4 or 4.6%).

In a control reaction (VIII), benzene was hydroalkylated in comparablemanner except that 100% of the hydroalkylating quantity of hydrogen (139parts per 100 parts of benzene) was admitted to the single stagereactor. The inlet temperature was 150 C. (300 F.) and the temperaturerose to over 220 C. (428 E). The product stream after 28 hours was asset forth supra.

Comparison of typical Example VII of this invention with control ExampleVIII, which yields substantially the same cyclohexylbenzene content(31.0% v. 32.5%) reveals that in experimental Example VII, theundesirable cyclohexylbenzene impurities were substantially decreased bya factor of more than two (G/31.0 or 1.6% v. 1.1/ 32.5 or 3.4%) comparedto control Example VIII; and the undesirable methylcyclopentane contentwas decreased by a factor of about 5 (0.24% v. 1.2%).

Examples yIX-XI In a third series of comparative examples,hydroalkylation of benzene was carried out over a catalyst comprising22% cobalt dispersed on a rare earth exchanged zeolite Y catalyst thathad been calcined at 800 C. in air and then reduced in the unit with aflow of hydrogen at 480 C. at atmospheric pressure. The benzene used waspretreated with sodium to remove all forms of oxygen-containingcomponents and then pumped over calcined 4A molecular sieves at roomtemperature before entering the reactor. The benzene was charged at 2LHSV together with deoxygenated hydrogen. All the hydrogen added wasconsumed and the rate of hydrogen addition was used to control theextent of the reaction. The pressure on the unit averages 250 p.s.i.g.

The unit was operated with an average 1.27 weight units of hydrogenadded per 100 units of benzene. The hydrogen was completely consumed inthe rst few inches of the 12-inch depth bed of catalyst, based on thetemperature rise across the catalyst bed. The inlet temperature averaged115 C. with the maximum temperature averaging 205 C. The product iscollected over a 38- hour period (Example IX).

In Example X, this product is then passed through the reactor a secondtime at 2 LHSV together with 0.83 units of hydrogen and an inlettemperature of 137 C. and a maximum temperature of 195 C. caused by theheat of reaction. Product from the second pass is collected (Example X).

In Example XI, the same catalyst is operated 'with 2.44 units ofhydrogen added per 100 units of benzene. The inlet temperature to thecatalyst is 100 C. and the average maximum temperature is 230 C.(Example XI).

The following table sets forth the composition of the products collectedin terms of weight percent of product.

Product IX X XI 1 Total hydrogen units reacted per 100 units benzene 1.27 0. 83 2. 44 Methylcyclopentane 0. 40 0. 64 1. 44 Cyclohexane 9. 3315. 42 18. 07 Beuren@ 69. 72 51. 31 45. 50 Cyclohexylbenzeneimpurities.- 0.45 0. 62 1. 16 Cyclohexybenzene 15. 18 21. 17 21. 61Dicyclohexylbenzene impurities 0. 12 0.34 0.62 Meta and orthodicyclohexylbenzene.- 2. 45 4. 62 6.81 Para-dicyclohexylbenzene- 2. 235. 21 3. 96 Tricyclohexylbenzene 0. 08 0. 64 0. 79

l Control.

It is apparent that when this cobalt on rare earth exchanged zeoliteCatalyst is operated with multiple hydrogen additions and control overthe maximum temperature that (a) the ratio of methylcyclopentane toCyclohexane is reduced (e.g. from 0.08 in Example XI to 0.041 in ExampleX) (b) the amount of 'by-products (impurities) boiling close to thecyclohexylbenzene is reduced (e.g. percent of CHB impurities in the CHBfraction is reduced from 5.1 percent in Example XI to 2.9 percent inExample X) and (c) the percent of paradicyclohexylbenzene in thedicyclohexylbenzene fraction is desirably increased (e.g. 35 percentp-DCHB in the DCHB fraction, including impurities, in Example XI versus51 percent p-DCHB in the DCHB fraction in Example X). It is apparentthat the product of Example X would be a preferred stock over theproduct of Example XI as a feed to a unit for the recovery ofpara-dicyclohexylbenzene, (d) when the temperature is controlled such asby multiple hydrogen injections, the hydrogen consumption is lowered forthe same rate of cyclohexylbenzene formation. The reaction 'becomes moreselective because less C6 naphthenes are formed.

Clearly products of Examples IX and X prepared by practice of theprocess of this invention, are superior to the product of controlExample XI.

Practice of the process of this invention may be apparent to thoseskilled in the art from inspection of the process flow sheet set forthin the accompanying schematic drawing and from the following descriptionwherein, as elsewhere in this specification, all parts are parts byweight unless otherwise stated.

In practice of this embodiment of the process of the invention, chargeincludes fresh benzene admitted through line 10, recycle benzeneadmitted through line 12 and fresh charge hydrogen admitted through line13. There may also be admitted through line 15 (although not done inthis embodiment) a recycle stream containing orthodicyclohexylbenzeneand meta-dicyclohexylbenzene.

The charge in line 16, containing 1.27 parts of hydrogen and parts ofbenzene, may be passed through exchanger 17 wherein it may be heated to115 C. (239 F.) at 500 p.s.i.g. by heat-exchange medium in line 18.

Hydroalkylation operation 19 contains (like the subsequenthydroalkylation operations) a bed of catalyst containing 22% cobalt on asupport, prepared by impregnating, with a solution of cobalt nitrate, azeolite Y matrix which had been ion-exchanged with -a solution of rareearth salt. The catalyst was calcined at 800 C. to yield a productcontaining 22% cobalt. The catalyst is reduced, prior to use, by contactwith owing hydrogen at 480 C.

Hydrogen is admitted to rst hydroalkylation operation 19 in amount of1.27 parts per 100 parts of benzene, this amount being 60% of thehydroalkylating quantity of hydrogen. As hydroalkylation proceeds at anLHSV of 2, the temperature increases in operation 19 to 205 C. (401 R).Product from the first hydroallcylation operation in line 20 containsthe following:

medium in line 23 to 137 C. (279 F.) and passed through line 24 tosecond hydroalkylation operation 25. Prior to admission to operation 25,it is mixed with 0.83 parts of hydrogen from line 26. This quantity ofhydrogen is 40% of the hydroalkylating quantity of hydrogen. Op-

tionally, if desired, the hydrogen in line 26 may be admitted to theupstream side of heat exchanger 22 so that the hydrogen may aid incooling the stream in line 20.

As hydroalkylation proceeds in operation 25 at an LHSV of 2, thetemperature increases to 195 C. (381 FJ. Product from the secondhydroalkylation operation in line 27 contains the following:

Components: Wt. percent Hydrogen Benzene 51.31 Methyl cyclopentane 0.64Cyclohexane 15.42 Cyclohexylbenzene impurities 0.62 Cyclohexylbenzene21.17 Dicyclohexylbenzene impurities 0.34 Dicyclohexylbenzene (Metaandortho) 4.62 (Para) 5.21 Tricyclohexylbenzenes 0.64

It will be apparent that it is unexpected that the high conversion of21% unexpectedly yields a high-purity cyclohexyl benzene containing only0.6% of cyclohexylbenzene impurities. (In a comparative example, anattempt to have the same high level of conversion by mixing all thehydrogen (2.44 parts per 100 parts of benzene) with the same totalquantity of charge prior to admission to the hydroalkylation operationwas unsuccessful. The temperature increased from 100 C. at the inlet to230 C.; and the product stream undesirably contained 1.16%cyclohexylbenzene impurities. This is unsatisfactory.)

Hydroalkylation product in line 27 is passed to separation operation 28wherein any trace of light gas may be separated. The separated gases arewithdrawn through line 14.

Flashed product liquid is passed through line 29 to heat exchanger 30,heated by steam in line 31, wherein it is heated before being passed tobenzene recovery operation 32. Overhead, containing 52.4 parts ofbenzene, 0.65 parts of methylcyclopentane, and 15.8 parts ofcyclohexane, is withdrawn through line 33, condensed in heat exchanger34 (cooled by water in line 35), and collected in condensate drum 36. Aportion of the benzene condensate is returned as pumped reflux throughline 37; and the remainder is passed through line 12 to a naphtheneremoval unit (not shown) to separate methyl cyclopentane and cyclohexanebefore being recycled to operation 19. If desired, a portion of thecondensate may be withdrawn through line 38.

Bottoms in tower 32 are reboiled in heat exchanger 39 by steam in line40 and returned to tower 32 through line 41. Net bottoms, in amount of33.3 parts, contain 21.6 parts of cyclohexylbenzene, 0.63 parts ofcyclohexylbenzene impurities, and 11 parts of dicyclohexylbenzene andtricyclohexyl benzenes and their impurities.

Net bottoms in line 42 are passed to heat exchanger 43 heated by steamin line 44 wherein they are heated and then passed to cyclohexyl benzenerecovery operation 45. Cycl'ohexylbenzene along with dicyclohexyl andthe methylcyclopentylbenzenes are withdrawn as overhead through line 46,condensed in heat exchanger 47 against water in line 48, and collectedin collection vessel 49. A portion of the condensate is passed as pumpedreflux to tower 45 through line 50. 22.25 parts of overhead, includingcyclohexylbenzene are Withdrawn through line 51.

Bottoms in tower 45 are reboiled in heat exchanger 52 heated by steam inline 53 and returned to tower 45 through line 54. Net bottoms in line55, in lamount of 11.04 parts, may contain principallyortho-dicyclohexylbenzene and meta-dicyclohexylbenzene (in total amountof 4.72 parts), and 5.32 parts of para-dicyclohexylbenzene. Smallamounts (0.35 parts) of other components boiling in thedicyclohexylbenzene range may be present 10 including higher boilingcomponents typically tricyclohexyl benzenes.

In this preferred embodiment, net bottoms in line 55 are passed throughheat exchanger 56 heated by a stream in line 57 and passed todicyclohexyl benzene recovery operation 58. Bottoms are reboiled in heatexchanger 59 heated by a stream in line 60 and returned to dicyclohexylbenzene recovery tower 58 through line 61. Net bottoms in line 62 may beessentially tricyclohexyl benzenes.

Overhead from tower 58 is withdrawn through line 63, condensed in heatexchanger 64 against Water in line 65, and collected in collectionvessel 66. The dicyclohexylbenzenes passed to vessel 66 may contain51.5% of paradicyclohexylbenzene and 45.5% of ortho-dicyclohexylbenzeneand meta-dicyclohexylbenzene.

Pumped reflux is returned through line 67 to tower 58; and 10.4 partsare withdrawn through line 68.

5.2 parts of diluent isopropyl alcohol are admitted through line 69 andthe mixture is cooled to minus 10 C. (14 F.) in heat exchanger 70 byrefrigerant in line 71.

The cooled mixture of dicyclohexylbenzenes, now primarily a slurry ofsolid para-isomer in a liquid containing isopropyl alcohol and themeta-isomer, is passed to separation operation 72. Filtration at minus10 C. (14 F.) permits recovery of 3.8 part of para-dicyclohexylbenzenelter icake (containing 0.2 part of mixed orthoand meta-isomers).Isopropanol is admitted through line 73 to slurry the lter cake; and theslurry is withdrawn from collector 74 and passed through line 75 atminus 10 C. (14 F.) to lter 76.

Filtrate from lilter 76, containing principally isopropanol, iswithdrawn through line 77; and `filter cake in amount of 4.0 parts iswithdrawn from collector 78 through line 79. Para-dicyclohexylbenzene inline 79 may be recovered in amount of 3.8 parts.

Filtrate from filtration operation 72 is Withdrawn at minus 10 C. (14F.) through line 80. This filtrate contains principallymeta-dicyclohexylbenzene, ortho-dicyclohexybenzene, isopropanol, andsmall amounts of para-dicyclohexylbenzene (1.6 parts) and otherimpurites (0.3 parts.) The filtrate in line 80 is passed through heatexhanger 81 heated by steam in line 82, and then passed to isopropanoltower 83. Overhead isopropanol in line 84 may be condensed in heatexchanger 85 (cooled by water in line 86) and collected in vessel 87. Aiirst portion of the condensed isopropanol may be pumped as pumpedreflux through line 88 to tower 83. A second portion may be passedthrough line 89 to line 73. An aliquot of the isopropanol in line 89 maybe passed through lines 9- and 69 to line 68. Isopropanol may be addedor withdrawn, as necessary, through line 91.

Bottoms from tower 83 may be reboiled in heat exchanger 92 heated bysteam in line 93 and returned through line 94 to tower 83. Net bottoms,stripped orthoand meta-dicyclohexyl benzenes, may be withdrawn throughline 95. Orthoand meta-dicyclohexyl benzenes may be withdrawn from, oradded to, the system through line 96. Orthoand meta-dicyclohexylbenzenesmay (after a drying operation not shown) optionally be passed throughline 15 to join with the charge dicyclohexyl benzenes in line 11.

The use of this novel process yields hydroalkylation reaction eluent inline 29 which desirably contains substantially decreased proportions ofundesirable cyclohexylbenzene impurities (dicyclohexyl andmethylcyclopentylbenzenes) and naphthenes.

Use of the novel process permits hydroalkylation to be carried out withliberation, during hydroalkylation, of much less heat per unit ofcyclohexyl benzene formed than is obtained by prior art practice. Themeans that more throughput can be passed through a reactor; or

that a reactor can be made smaller; or that it can be operated at lowertemperatures to give the desired yield; or that it can be operated atthe same temperature with higher effective yield.

In the prior art, a limiting determinant on the reaction has been theability to control heat transfer in the hydroalkylation reactor to keepwithin desired temperature range and thus minimize formation ofundesirable byproducts.

The novel process is characterized by the ability to operate underconditions permitting attainment of high concentrations of cyclohexylbenzene (up to e.g. 30%) and to operate with decreased heat liberationdue e.g. to decreased formation of exothermically produced dicyclohexylbenzenes.

It is a feature of the process of this invention that when thehydroalkylation is carried out at a lower temperature, the ratio of thepara to the meta dicyclohexylbenzenes is increased. The paradicyclohexylbenzene can be readily separated and purified from the mixeddicyclohexylbenzene fraction. Thus to increase para-dicyclohexylbenzenerecovery, it is advantageous to operate at low hydroalkylationtemperature in order to take advantage of the more favorable isomerratio in the dicyclohexylbenzene fraction. The percent para DCHB in theDCHB fraction can be increased from about 35% when the maximumtemperature is greater than 230 C. to greater than 65% when the maximumreactor temperature is less than 130 C.

By hydroalkylating in stages with multiple additions of hydrogen, theheat liberated can be controlled without excessive temperatures beingreached. 'Ihus by avoiding high temperatures more favorable productselectivities are obtained.

Although this invention has been illustrated by reference to specificembodiments, it will be apparent to those skilled in the art thatvarious changes and modications may be made which clearly fall withinthe scope of this invention.

We claim:

1. The process for hydroalkylating a charge mononuclear aromatichydrocarbon with a hydroalkylating quantity of hydrogen which comprisespassing said charge hydrocarbon and a first portion of saidhydroalkylating quantity of hydrogen through a rst hydroalkylationoperation at hydroalkylation conditions thereby forming a partiallyhydroalkylated stream;

withdrawing said partially hydroalkylated stream from said firsthydroalkylation operation;

passing said partially hydroalkylated stream through at least onesubsequent hydroalkylation operation at hydroalkylation conditions;

passing the remainder of said hydroalkylating quantity of hydrogen tosaid subsequent hydroalkvlation operation;

maintaining said partially hydroalkylated stream during passage intoeach hydroalkylation operation, at hydroalkylation conditions therebyforming product hydroalkylate; and

said hydroalkylation operations.

withdrawing product hydroalkylate from the last of 2. The process forhydroalkylating a charge mononuclear aromatic hydrocarbon as claimed inclaim 1 wherein said tirst portion is %75 of the hydroalkylatingquantity of hydrogen.

3. The process for hydroalkylating a charge mononuclear aromatichydrocarbon as claimed in claim 1 wherein said tirst portion is about50% of the hydroalkylating quantity of hydrogen.

4. The process for hydroalkylating a charge mononuclear aromatichydrocarbon as claimed in claim k1 wherein substantially the samepercentage of the hydroalkylating quantity of hydrogen is added to eachof said first hydroalkylation operation and said subsequenthydroalkylation operations.

5. The process for hydroalkylating a charge mononuclear aromatichydrocarbon as claimed in claim 1 wherein hydroalkylation is carried outin two hydroalkylation operations.

6. The process for hydroalkylating a charge mononuclear aromatichydrocarbon as claimed in claim 1 wherein hydroalkylation is carried outin two hydroalkylation operations and 40%-70% of the hydroalkylatingquantity of hydrogen is admitted to the first hydroalkylation operationand 30%60% of the hydroalkylating quantity of hydrogen is admitted tothe second hydroalkylation operation.

7. The process for hydroalkylating a charge hydrocarbon aromatichydrocarbon with a hydroalkylating quantity of hydrogen as claimed inclaim 1 wherein the temperature of hydroalkylation is C.-250 C.

8. The process for hydroalkylating a charge hydrocarbon aromatichydrocarbon with a hydroalkylating quantity of hydrogen as claimed inclaim 1 wherein the temperature of hydroalkylation is -2l0 C.

9. The process for hydroalkylating a charge hydrocarbon aromatichydrocarbon with a hydroalkylating quantity of hydrogen as claimed inclaim 1 wherein the liquid hourly space velocity in each of thehydroalkylation operations is 1-15.

10. The processs for hydroalkylating a charge hydrocarbon aromatichydrocarbon with hydroalkylating quantity of hydrogen as claimed inclaim 1 wherein the partial pressure of hydrogen during hydroalkylationis 100-1500 p.s.i.g.

11. The process for hydroalkylating a charge mononuclear aromatichydrocarbon With a hydroalkylating quantity of hydrogen which comprises:

passing said charge hydrocarbon through a plurality of hydroalkylationoperations at hydroalkylation conditions;

passing a portion of said hydroalkylating quantity of hydrogen to eachof said hydroalkylating operations; cooling said partiallyhydroalkylated stream during said hydroalkylating operations; and

withdrawing product hydroalkylate from the last of said hydroalkylationoperations.

12. The process for hydroalkylating a charge mononuclear aromatichydrocarbon with a hydroalkylating quantity of hydrogen which comprisespassing said charge hydrocarbon through a lirst and at least onesubsequent hydroalkylation operation at hydroalkylation conditions;

passing a portion of said hydroalkylating quantity of hydrogen to eachof said hydroalkylating operations;

cooling said partially hydroalkylated stream prior to addition to eachof said susequent hydroalkylation operations; and

withdrawing product hydroalkylate from the last of said hydroalkylationoperations.

13. The process for hydroalkylating a charge mononuclear aromatichydrocarbon with a hydroalkylating quantity of hydrogen which comprises:

passing a portion of said hyidroalkylating quantity least one subsequenthydroalkylation operation at hydroalkylation conditions passing aportion of said hydroalkylating quantity of hydrogen to each of saidhydroalkylation operations;

cooling said partially hydroalkylated stream to 80 C.-

200 C. prior to admission to each of said subsequent hydroalkylationoperations; and

withdrawing product hydroalkylate from the last of said hydroalkylationoperations.

14. The process for hydroalkylating benzene with a hydroalkylatingquantity of hydrogen which comprises passing said charge benzene and40%-70% of the hydroalkylating quantity of hydrogen through a rsthydroalkylation operation at hydroalkylation condi- M tions including atemperature of 80 C.200 C. References Cited thereby forming a partiallyhydroalkylated stream; withdrawing said partially hydroalkylated streamfrom UNITED STATES PATENTS said first hydroalkylatign Operation3,153,678 10/1964 Logemann 260-667 cooling said withdrawn partiallyhydroalkylated r. 3,317,611 5/1967 LOuVaI et aL 26o-668 F product Streamto 80 C 200 C o Slaugh et al. R

passing said cooled stream and 30%-60% of the hydroalkylating quantityof hydrogen to a second hy- CURTIS R DAVIS Primary Exammer droalkylationoperation at hydroalkylating condi- Us C1 XR tion thereby forming aproduct hydroalkylate; and 10 260 667 670 withdrawing said producthydroalkylate.

' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,3,784,617 Dated January 8, 197i# IWEMIONQR. N. SUGGITT, J. IVI. CRONE,JR. AND ALFRED ARKELL It is certified that error appears in theabove-identified patent and that saidALetters Patent are'herebycorrected as shown below:

Col. '2 Table reads components should read component Col. 6, line 3"benezne" Should read --T-benzene-n- Col. ll, `Claim l v -l last line-the last two lines should be reversed .4 so as to read --withdrawngproduct hydroalkylate from `the last of said hydroalkylaton operations.A

`Signedand sealed this 6th day of August 1974.

(SEAL)v v Attest:

McCOY M. GIBSON, JR. l C. MARSHALL DANN Attestng Officer CommissionerofPatents

